Grounding impedance determination method and device and electronic equipment

Abstract

The invention discloses a grounding impedance determination method and device and electronic equipment. The method comprises the steps that ground surface potential distribution is determined, and the ground surface potential distribution represents potential changes generated by the ground surface under the condition that an underground cable tunnel is short-circuited; according to the surface potential distribution, a first position of a current electrode and a second position of a voltage electrode for impedance measurement of the cable tunnel are determined, an electric connection loop exists between the current electrode and the voltage electrode, and the target distance between the first position and the second position is smaller than a preset distance; performing current injection processing on a predetermined current injection point on the cable tunnel by adopting a predetermined short-circuit fault simulation mode, obtaining a measurement current at a current electrode, and obtaining a measurement voltage at a voltage electrode; a ground impedance of the cable tunnel is determined based on the measured current and the measured voltage. The technical problem that the electrode wiring distance is too large in cable tunnel grounding impedance measurement in the prior art is solved.

Description

Technical Field

[0001] This application relates to the field of power systems, and more particularly, to a method, apparatus, and electronic device for determining ground impedance. Background Art

[0002] As an important part of urban power grid construction, cable tunnels play an important role in transmitting electricity. Whether the grounding grid of a cable tunnel is reliable directly affects the operation safety of cables, electrical equipment, etc. in the cable tunnel. Ground resistance is one of the important indicators for evaluating the reliability and safety of the grounding grid. Usually, the grounding impedance of a cable tunnel is estimated by using a grounding impedance test method. The length of a cable tunnel is usually long, which makes the workload large and the test efficiency low when testing the grounding impedance of the cable tunnel in related technologies. The tunnel is not suitable for testing the grounding impedance of the cable tunnel.

[0003] In view of the above problems, no effective solution has been proposed yet.

[0004] Application Content

[0005] Embodiments of this application provide a method, apparatus, and electronic device for determining ground impedance to at least solve the technical problem of excessive electrode wiring distance in measuring the ground impedance of a cable tunnel in related technologies.

[0006] According to one aspect of the embodiments of this application, a method for determining ground impedance is provided, including: determining the surface potential distribution, where the surface potential distribution represents the potential change on the surface when a short circuit occurs in the underground cable tunnel; determining the first position of the current electrode and the second position of the voltage electrode for impedance measurement of the cable tunnel according to the surface potential distribution, where there is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel; performing current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method, obtaining a measured current at the current electrode, and obtaining a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground; determining the ground impedance of the cable tunnel based on the measured current and the measured voltage.

[0007] Optionally, the surface potential distribution includes a first potential distribution and a second potential distribution. Determining the first position of the current electrode and the second position of the voltage electrode for impedance measurement of the cable tunnel according to the surface potential distribution includes: performing current injection processing on the current injection point to determine the first potential distribution; determining the first position of the current electrode according to the first potential distribution; determining the second potential distribution when the current electrode is inserted at the first position; determining the second position of the voltage electrode according to the second potential distribution.

[0008] Optionally, determining a first position of a current electrode according to a first potential distribution includes: determining a first surface potential corresponding to a surface mapping point of a current injection point; based on the first potential distribution, determining a first position that causes the first surface potential to decrease to a first predetermined potential threshold.

[0009] Optionally, determining a second position of a voltage electrode according to a second potential distribution includes: determining a second surface potential corresponding to a surface mapping point of a current injection point, where the second surface potential is determined under the condition that a current electrode is inserted at the first position; based on the second potential distribution, determining a second position that causes the second surface potential to decrease to a second predetermined potential threshold.

[0010] Optionally, an included angle between a first connection line between the first position and the surface mapping point of the current injection point and a second connection line between the second position and the surface mapping point is greater than a predetermined angle threshold.

[0011] Optionally, performing current injection processing on a predetermined current injection point on a cable tunnel by using a predetermined short - circuit fault simulation method to obtain a measured current at the current electrode and a measured voltage at the voltage electrode, including: determining predetermined currents at multiple measurement frequencies according to the short - circuit fault simulation method, where the multiple measurement frequencies are determined to avoid power frequency interference; using the predetermined currents at multiple measurement frequencies to perform current injection processing on the current injection point to obtain measured currents and measured voltages respectively corresponding to the multiple measurement frequencies.

[0012] Optionally, determining the grounding impedance of the cable tunnel based on the measured current and the measured voltage includes: determining measured impedances respectively corresponding to multiple measurement frequencies according to the measured currents and measured voltages respectively corresponding to the multiple measurement frequencies; performing an averaging process on the measured impedances respectively corresponding to the multiple measurement frequencies to obtain an average impedance; determining the grounding impedance based on the average impedance.

[0013] Optionally, the short - circuit current in the cable tunnel is also derived through the grounding grid of a substation connected to the cable tunnel. Determining the grounding impedance based on the average impedance includes: determining a shunt coefficient based on the short - circuit current derived through the grounding grid of the cable tunnel and the short - circuit current derived through the grounding grid of the substation; correcting the average impedance according to the shunt coefficient to determine the grounding impedance.

[0014] According to another aspect of the embodiments of the present application, a ground impedance determination device is provided, including: a surface potential distribution determination module for determining the surface potential distribution, where the surface potential distribution represents the potential change generated on the surface in the case of a short circuit in an underground cable tunnel; a position determination module for determining a first position of a current electrode for impedance measurement of the cable tunnel and a second position of a voltage electrode according to the surface potential distribution, where there is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel; a measurement result determination module for performing current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method to obtain a measured current at the current electrode and a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground; and a ground impedance determination module for determining the ground impedance of the cable tunnel based on the measured current and the measured voltage.

[0015] According to another aspect of the embodiments of the present application, an electronic device is provided, including: one or more processors and a memory, where the memory is used to store one or more programs, and when the one or more programs are executed by the one or more processors, the one or more processors are caused to implement the ground impedance determination method according to any one of the above.

[0016] In the embodiments of the present application, by determining the surface potential distribution, where the surface potential distribution represents the potential change generated on the surface in the case of a short circuit in an underground cable tunnel; determining a first position of a current electrode for impedance measurement of the cable tunnel and a second position of a voltage electrode according to the surface potential distribution, where there is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel; performing current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method to obtain a measured current at the current electrode and a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground; and determining the ground impedance of the cable tunnel based on the measured current and the measured voltage. The purpose of determining the positions of the current electrode and the voltage electrode based on the surface potential change and obtaining the ground impedance of the cable tunnel is achieved, and the technical effect of improving the accuracy of the measured value of the ground impedance of the cable tunnel is realized, thereby solving the technical problem of too large electrode wiring distance in the measurement of the ground impedance of the cable tunnel in the related art. Description of the Drawings

[0017] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0018] Figure 1 is a flowchart of an optional method for determining ground impedance provided by an embodiment of the present application;

[0019] Figure 2 is a schematic diagram of a first shielded cable tunnel of an optional method for determining ground impedance provided by an embodiment of the present application;

[0020] Figure 3 is a schematic diagram of a first earthing grid of a cable tunnel of an optional method for determining ground impedance provided by an embodiment of the present application;

[0021] Figure 4 is a schematic diagram of the soil stratification structure near a cable tunnel of an optional method for determining ground impedance provided by an embodiment of the present application;

[0022] Figure 5 is a schematic diagram of a second earthing grid of a cable tunnel of an optional method for determining ground impedance provided by an embodiment of the present application;

[0023] Figure 6 is a schematic diagram of a surface potential observation plane of an optional method for determining ground impedance provided by an embodiment of the present application;

[0024] Figure 7 is a schematic diagram of a second shielded cable tunnel of an optional method for determining ground impedance provided by an embodiment of the present application;

[0025] Figure 8 is a schematic diagram of an injection point of a second shielded cable tunnel of an optional method for determining ground impedance provided by an embodiment of the present application;

[0026] Figure 9 is a schematic diagram of an optional device for determining ground impedance provided by an embodiment of the present application. Detailed implementation manners

[0027] In order to enable those skilled in the art to better understand the solutions of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0028] It should be noted that the terms "first", "second", etc. in the description, claims and the above-mentioned drawings of the present application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily limit to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0029] For the convenience of description, some nouns or terms related to the embodiments of the present application are described below:

[0030] Grounding impedance refers to the degree of obstruction of the grounding system to current when current flows into the earth through the grounding system. The magnitude of the grounding impedance directly affects the safety performance of the equipment during lightning strikes and electrical failures and the stable operation of the system, and is a key parameter for measuring the performance of the grounding system.

[0031] A shield-type high-voltage cable tunnel is an underground tunnel constructed by the shield method for laying and protecting high-voltage cables, which has the advantages of strong structure, strong environmental adaptability, diversity of cable laying, convenient maintenance and repair, high safety and fast construction speed, and is commonly used in the construction of cable tunnels in urban dense areas or areas with complex geological conditions.

[0032] The three-electrode method refers to measuring the potential difference between the voltage electrode and the grounding device by arranging three electrodes (i.e., the grounding device, the current electrode and the voltage electrode) on the ground, and then obtaining the grounding impedance of the grounding device, which is used to evaluate and monitor the performance of the grounding systems of power facilities, buildings, etc.

[0033] According to the embodiments of the present application, an embodiment of a method for determining grounding impedance is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0034] Figure 1 is a flowchart of an optional method for determining grounding impedance provided according to the embodiments of the present application, as Figure 1 shown, the method includes the following steps:

[0035] Step S102, determining the surface potential distribution, where the surface potential distribution represents the potential change on the surface in the case of a short circuit in the underground cable tunnel.

[0036] It can be understood that when a short - circuit fault occurs in the cable tunnel, a large short - circuit current will enter the ground through the grounding grid, causing the surface potential to change. The surface potential distribution is determined through the surface potential observation surface above the tunnel. When a short - circuit fault occurs, determining the surface potential distribution near the short - circuit point can provide data support for the performance evaluation of the cable tunnel grounding grid.

[0037] Optionally, when a short - circuit fault occurs in the cable in the cable tunnel, a large amount of short - circuit current will dissipate into the ground through the cable metal sheath and the grounding grid connected to it. Due to the dissipation of current in the ground, the surface potential will change accordingly. The surface potential distribution can be obtained through simulation by setting up a surface potential observation surface on the ground. By simulating the surface potential distribution, the potential distribution law near the fault point can be obtained, which is conducive to accurately evaluating, designing, and maintaining the grounding grid to ensure the safe operation of the power system.

[0038] Step S104, determine the first position of the current electrode and the second position of the voltage electrode for impedance measurement of the cable tunnel according to the surface potential distribution. Among them, there is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel;

[0039] It can be understood that according to the size of the grounding grid of the cable tunnel, the predetermined distance between the current electrode and the voltage electrode is determined. Based on the surface potential distribution, according to the requirement that the effective distance (i.e., the target distance) between the first position where the current electrode is placed and the second position where the voltage electrode is placed and the grounding grid is less than the above - mentioned predetermined distance, determine the first position for placing the current electrode and the second position for placing the voltage electrode, and form an electrical connection loop between the current electrode and the voltage electrode through a wire. By scientifically selecting the layout positions of the current electrode and the voltage electrode, not only the test process of the cable tunnel grounding impedance is simplified, but also the accuracy and reliability of the test results are ensured.

[0040] Optionally, in order to reduce the error of the grounding impedance measurement result, in the grounding impedance measurement method in the related art, the current electrode and the voltage electrode usually need to be placed at a position 4 - 5 times the diagonal length away from the grounding grid. Therefore, the above - mentioned predetermined distance is 4 - 5 times the diagonal length of the grounding grid. The effective distance (i.e., the target distance) between the first position where the current electrode is placed and the second position where the voltage electrode is placed and the grounding grid refers to the minimum layout distance that can ensure the measurement accuracy and reduce the measurement error between the current electrode and the voltage electrode and the grounding grid, that is, the position where the potential drops close to 0 obtained through potential distribution simulation. When measuring the grounding impedance of the cable tunnel, using the effective distance instead of the predetermined distance can not only ensure the accuracy of the measurement result, but also reduce the workload and cost and improve the test efficiency.

[0041] Optionally, the above cable tunnel can be a shield - type cable tunnel, a pipe - jacking type cable tunnel, an integrated utility tunnel, or a composite - structure cable tunnel.

[0042] In an alternative embodiment, the surface potential distribution includes a first potential distribution and a second potential distribution. According to the surface potential distribution, determining a first position of the current electrode for impedance measurement of the cable tunnel and a second position of the voltage electrode includes: performing current injection processing on the current injection point to determine the first potential distribution; determining the first position of the current electrode according to the first potential distribution; determining the second potential distribution when the current electrode is inserted at the first position; and determining the second position of the voltage electrode according to the second potential distribution.

[0043] It can be understood that a suitable current injection point is selected in the cable tunnel to simulate a short - circuit fault of the cable tunnel and simulate the surface potential distribution to obtain the first potential distribution. According to the first potential distribution, the effective distance (i.e., the target distance) between the first position where the current electrode is placed and the grounding grid is obtained, and according to the above - mentioned target distance, the first position of the current electrode arrangement is determined. After the current electrode is arranged, the surface potential will change, and the surface potential distribution is simulated again to obtain the second surface potential distribution. According to the second potential distribution, the effective distance (i.e., the target distance) between the second position where the voltage electrode is placed and the grounding grid is obtained, and based on the above - mentioned target distance, the second position of the voltage electrode arrangement is determined. By determining the potential distribution twice, the arrangement positions of the current electrode and the voltage electrode can be selected more accurately, thereby reducing the measurement error and ensuring the accuracy and reliability of the measurement results.

[0044] In an alternative embodiment, determining the first position of the current electrode according to the first potential distribution includes: determining a first surface potential corresponding to the surface mapping point of the current injection point; and determining the first position that makes the first surface potential drop to a first predetermined potential threshold based on the first potential distribution.

[0045] It can be understood that current is injected at the current injection point, and the first surface potential and the first potential distribution of the surface mapping point of the current injection point are measured. According to the first surface potential and the first predetermined potential threshold, the maximum allowable surface potential in the current electrode arrangement area is obtained. Based on the maximum allowable surface potential in the current electrode arrangement area and according to the first potential distribution, the first position of the current electrode arrangement is determined. By accurately arranging the position of the current electrode, the influence of the current electrode on the surface potential is avoided, ensuring the accuracy of the grounding impedance measurement. At the same time, the problem of excessive test difficulty caused by the current electrode being too far from the grounding grid is avoided.

[0046] Optionally, when current flows into the grounding grid from the current injection point, the surface potential will change, and this change in potential reflects the current dissipation in the soil. To reduce the influence of the current electrode itself on the surface potential distribution and thus reduce the error in measuring the grounding impedance, a minimum potential threshold (i.e., the first predetermined potential threshold) is set, such as 5% of the maximum allowable surface potential. The current electrode is arranged at the position where the surface potential drops to the first predetermined potential threshold, reducing the influence of the introduction of the current electrode on the surface potential distribution and avoiding the problems of high working difficulty and high cost caused by the need to place the current electrode too far away in related methods.

[0047] In an alternative embodiment, determining the second position of the voltage electrode according to the second potential distribution includes: determining the second surface potential corresponding to the surface mapping point of the current injection point, where the second surface potential is determined in the case of inserting the current electrode at the first position; based on the second potential distribution, determining the second position that causes the second surface potential to drop to the second predetermined potential threshold.

[0048] It can be understood that after inserting the current electrode at the first position, the surface potential will change. The surface potential is re-measured to obtain the second surface potential of the surface mapping point of the current injection point and the second potential distribution. According to the second surface potential and the second predetermined potential threshold, the maximum allowable surface potential in the voltage electrode arrangement area is obtained. Based on the maximum allowable surface potential in the voltage electrode arrangement area and according to the second potential distribution, the second position of the voltage electrode arrangement is determined. Determining the second position of the voltage electrode according to the second potential distribution after introducing the current electrode can ensure that the voltage electrode is in an area close to zero potential, reducing the errors caused by mutual inductance and uneven potential distribution in voltage measurement and improving the measurement accuracy.

[0049] Optionally, when the current electrode is inserted at the first position, the surface potential will change. To obtain the accurate potential difference of the grounding grid relative to infinity and thus accurately measure the grounding impedance, the second position of the voltage electrode should be selected at the zero potential position, i.e., infinity. To reduce the test difficulty, a minimum potential threshold (i.e., the second predetermined potential threshold) is set, such as 5% of the maximum allowable surface potential. The voltage electrode is arranged at the position where the surface potential drops to the second predetermined potential threshold, which can control the error within a reasonable range and make the voltage measured between the grounding grid and the voltage electrode approximately equal to the potential of the grounding grid relative to the infinite point. Determining the second position of the voltage electrode by re-measuring the surface potential distribution after introducing the current electrode optimizes the voltage electrode arrangement scheme and improves the measurement accuracy and test efficiency.

[0050] In an alternative embodiment, the included angle between the first connection line between the first position and the surface mapping point of the current injection point and the second connection line between the second position and the surface mapping point is greater than a predetermined angle threshold.

[0051] It can be understood that a predetermined angle threshold is set based on the minimum degree of mutual interference between the current electrode and the voltage electrode. Based on the above-mentioned current injection point position and the first position of the current electrode, a first connection line is determined, that is, the straight-line path from the surface mapping point of the current injection point to the first position of the current electrode. Based on the above-mentioned current injection point position and the second position of the voltage electrode, a second connection line is determined, that is, the straight-line path from the surface mapping point of the current injection point to the second position of the voltage electrode. Compare the size of the angle between the first connection line and the second connection line with the predetermined angle threshold. If the angle between the first connection line and the second connection line is greater than the predetermined angle threshold, the second position of the voltage electrode meets the requirements; if the angle between the first connection line and the second connection line is less than the predetermined angle threshold, the second position of the voltage electrode does not meet the requirements, and the second position of the voltage electrode needs to be reselected. By ensuring that the angle between the first connection line and the second connection line is greater than the predetermined angle threshold, the interference of the current electrode on the voltage electrode measurement can be significantly reduced, thereby improving the accuracy of the test results.

[0052] Optionally, the predetermined angle threshold is determined according to the degree of mutual interference between the current electrode and the voltage electrode. Since the magnetic field generated by the current electrode will directly affect the voltage electrode, causing a mutual inductance effect, the smaller the angle between the first connection line and the second connection line, the greater the electromagnetic interference caused. When determining the second position of the voltage electrode, not only the second predetermined potential threshold needs to be considered, but also the angle between the first connection line and the second connection line needs to be taken into account to determine whether the angle meets the requirements of the predetermined angle threshold. If the angle is less than the predetermined angle threshold, the second position of the voltage electrode should be adjusted to ensure that the angle between the two connection lines is large enough, thereby reducing the mutual inductance effect between the current electrode and the voltage electrode. By ensuring that the included angle between the current electrode and the voltage electrode is greater than the predetermined angle threshold, the mutual inductance effect between the current electrode and the voltage electrode can be significantly reduced, enabling the electrode position to more truly reflect the impedance characteristics of the grounding grid, avoiding measurement result deviations caused by improper positions of the current electrode and the voltage electrode, and thus improving the reliability of the grounding impedance test.

[0053] Step S106, perform current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method, obtain a measured current at the current electrode, and obtain a measured voltage at the voltage electrode, wherein the current injection point forms a loop with the current electrode and the voltage electrode through the ground;

[0054] It can be understood that the current injection point is selected, and current is injected at the current injection point to simulate a predetermined cable tunnel short - circuit fault. When the current is injected from the current injection point, it will flow through the ground to the current electrode, jointly forming a test loop with the voltage electrode. The current is measured at the current electrode to obtain the measured current, which is used to reflect the impedance characteristics of the grounding grid; the voltage is measured at the voltage electrode to obtain the measured voltage, which is used to represent the potential change caused by the current flowing through the grounding grid. By simulating the short - circuit fault, the current distribution and potential change in the cable tunnel under fault conditions can be more realistically simulated, making the test results closer to the actual situation and improving the accuracy and practicality of the test.

[0055] Optionally, based on the layout of the cable tunnel, the distribution of the cables, and the structure of the ground grid, the current injection point is selected. The selection of the current injection point should consider typicality and representativeness, safety, and current injection capacity. Typicality and representativeness mean that the current injection point should be selected in a typical area that can represent the entire grounding grid to ensure that the injected current can uniformly pass through each part of the grounding grid, so that the test results can reflect the overall current - dissipation characteristics of the grounding grid. Safety means that a safe distance should be maintained between the current injection point and surrounding equipment, cables, or other sensitive facilities to avoid potential safety hazards to other equipment caused by current injection during the test. Current injection capacity means that the current injection point should be able to withstand the current injection required for the test without damaging the electrical characteristics of the current injection point due to excessive current. By accurately selecting the current injection point, the test results can truly reflect the performance of the grounding grid, providing reliable data support for the safety assessment and maintenance of power facilities.

[0056] In an alternative embodiment, a predetermined short - circuit fault simulation method is adopted to perform current injection processing on a predetermined current injection point on the cable tunnel, obtaining the measured current at the current electrode and the measured voltage at the voltage electrode, including: determining the predetermined currents at multiple measurement frequencies according to the short - circuit fault simulation method, where the multiple measurement frequencies are determined to avoid power - frequency frequency interference; using the predetermined currents at multiple measurement frequencies to perform current injection processing on the current injection point, obtaining the measured current and measured voltage corresponding to each of the multiple measurement frequencies respectively.

[0057] It can be understood that the maximum short - circuit current of the cable tunnel is determined. To avoid power - frequency interference, multiple groups of frequency values close to the predetermined power - frequency are selected as the frequencies for current injection. The predetermined currents at the above - mentioned multiple groups of frequencies close to the predetermined power - frequency are determined as the injection currents. The above - mentioned multiple groups of predetermined currents at frequencies close to the predetermined power - frequency are respectively injected into the current injection point, and the measured current and measured voltage corresponding to each of the multiple measurement frequencies are obtained. Multi - frequency testing can cover a wider range of electrical characteristics, provide more comprehensive test results, thereby formulating a more scientific and effective cable tunnel maintenance strategy to ensure the long - term stable and safe operation of the cable tunnel grounding grid.

[0058] Optionally, in an actual power system, different frequencies will affect the measurement results of the grounding impedance. The inductance effect, capacitance effect, and soil impedance characteristics of the grounding grid will all cause different grounding impedance measurement results when injecting the same magnitude of current at different frequencies. The above-mentioned inductance effect refers to the fact that the metal components in the grounding grid will generate inductance, and under high-frequency conditions, the inductance effect is more significant, resulting in an increase in the grounding impedance measurement results under high-frequency conditions. The above-mentioned capacitance effect refers to the fact that the capacitance between the grounding grid and the soil interface will affect the impedance measurement as the frequency changes. Under high-frequency conditions, the capacitance effect increases, which may lead to a decrease in the impedance measurement results. The above-mentioned soil impedance characteristics refer to the fact that the resistivity and dielectric properties of the soil will affect the measurement results of the grounding impedance. At the same time, changes in the moisture and conductivity in the soil will also affect the impedance characteristics of the grounding grid. Measure the grounding impedance of the grounding grid at different frequencies, identify and eliminate frequency-related interference factors in the test, so as to improve the accuracy of the test results.

[0059] Step S108, determine the grounding impedance of the cable tunnel based on the measured current and the measured voltage.

[0060] It can be understood that based on the measured current of the grounding grid and the measured voltage of the grounding grid, using Ohm's law, the grounding impedance of the cable can be obtained. By directly calculating the grounding impedance using the measured current and the measured voltage, accurate grounding impedance measurement results can be obtained, providing data support for evaluating the performance of the cable tunnel grounding grid under short-circuit faults.

[0061] In an optional embodiment, determining the grounding impedance of the cable tunnel based on the measured current and the measured voltage includes: determining the measured impedances corresponding to multiple measurement frequencies according to the measured currents and measured voltages corresponding to multiple measurement frequencies; performing mean processing on the measured impedances corresponding to multiple measurement frequencies to obtain a mean impedance; and determining the grounding impedance based on the mean impedance.

[0062] It can be understood that based on a predetermined power frequency, multiple groups of frequencies close to the predetermined power frequency are selected, and a predetermined current to be injected is determined. The predetermined currents at the above-mentioned multiple groups of frequencies close to the predetermined power frequency are respectively injected into the current injection points, and the measured currents and measured voltages corresponding to multiple measurement frequencies are obtained. Based on the measured currents and measured voltages corresponding to multiple measurement frequencies, the measured impedances corresponding to multiple measurement frequencies are obtained. Perform mean processing on the measured impedances corresponding to the above-mentioned multiple measurement frequencies to obtain a mean impedance, and correct the mean impedance to obtain the grounding impedance. By adopting the mean processing method, the influence of random errors in the measurement can be reduced, and the stability and reliability of the grounding impedance evaluation can be improved.

[0063] In an alternative embodiment, the short-circuit current in the cable tunnel is also derived through the grounding grid of the substation connected to the cable tunnel. Based on the mean impedance, the grounding impedance is determined, including: determining the shunt coefficient based on the short-circuit current derived through the grounding grid of the cable tunnel and the short-circuit current derived through the grounding grid of the substation; and correcting the mean impedance according to the shunt coefficient to determine the grounding impedance.

[0064] It can be understood that when a short-circuit fault occurs in the cable tunnel, part of the short-circuit current is derived through the grounding grid, and part of the current is derived through the grounding grid of the substation connected to the cable tunnel. By respectively determining the magnitudes of the above two parts of the current, the shunt coefficient of the current derived through the grounding grid is determined. Based on the above shunt coefficient, the mean impedance is corrected to obtain the grounding impedance. By correcting the mean impedance through the shunt effect coefficient, the grounding impedance of the cable tunnel can be evaluated more accurately, the interference of the substation grounding grid on the measurement result is eliminated, and more accurate data support is provided for system design and maintenance.

[0065] Optionally, due to the generally ultra-long and slender characteristics of the cable tunnel, its grounding grid must be able to effectively conduct the fault current into the ground while meeting the environmental requirements of the cable tunnel. The grounding grids of cable tunnels include natural grounding grids, artificial grounding grids, multi-level grounding grids, and sectional grounding grids, etc. A natural grounding grid refers to a grounding grid formed by using metal components in the structure of the cable tunnel itself, including the steel bar structure on the inner wall of the tunnel, metal brackets, continuous flat steel, and circular grounding steel bars, etc. An artificial grounding grid refers to a grounding grid set inside the tunnel or on the ground near the tunnel, such as vertically or horizontally arranged copper-clad steel grounding electrodes, copper strip grounding wires, etc., to enhance the current-dispersing ability of the grounding grid. A multi-level grounding grid refers to that for an ultra-long cable tunnel, a multi-level grounding grid needs to be set up, including special grounding grids at the starting shaft, receiving shaft, and inspection shaft, as well as the combination of natural and artificial grounding grids inside the tunnel, to ensure that the current evenly disperses into the ground at multiple points and improve the reliability of the overall grounding grid. A sectional grounding grid refers to that in a long-distance cable tunnel, the tunnel is divided into multiple sections, and each section is provided with its own grounding grid to ensure that the current can evenly disperse along the entire length of the tunnel and avoid local overvoltage or overcurrent. Based on the characteristics of the cable tunnel, different grounding grids are selected to ensure that the current-dispersing requirements of the cable tunnel are met and to maintain the safe and stable operation of the power system.

[0066] Optionally, when the power system is operating normally, the current flowing into the ground through the neutral point of the transformer is very small. However, when a short-circuit fault occurs in the power system, the voltage at the fault point drops suddenly, resulting in an increased potential difference between the fault point and the ground. As a result, a large amount of current flows into the ground via the grounding grid. The total short-circuit current will not all flow into a single grounding point and will be shunted within the system, entering the ground through different grounding points. For cable lines, when a short-circuit fault occurs, due to the triangular arrangement and cross-bonding design of the cables, the metal sheaths of the cables will form a closed loop, allowing part of the short-circuit current to return along this path instead of directly entering the ground. Therefore, a part of the short-circuit current will return to the neutral point of the transformer through the metal sheath layer of the cable line. At the same time, since the metal sheath of the cable is directly connected to the grounding grid, forming a low-impedance path, when a short-circuit fault occurs, most of the current will flow through the metal sheath loop and enter the ground through the grounding grid connected to the cable sheath. This path of entering the ground will have a greater impact on the ground potential rise, step voltage, and touch voltage near the grounding point. The grounding grid can be safely evaluated by measuring the grounding impedance, and corresponding maintenance and optimization can be carried out to improve the reliability of the power system.

[0067] Optionally, in the grounding impedance test of the cable tunnel, due to the presence of the cable sheath, part of the test current will be shunted through the cable sheath to the substation grounding grid, resulting in a deviation between the initially measured grounding impedance value and the actual value. To more accurately reflect the actual performance of the grounding grid, it is necessary to correct the initial grounding impedance result according to the shunt coefficient. The shunt coefficient is obtained based on the proportion of the tunnel short-circuit current flowing into the ground in the first conduction mode to the total short-circuit current. The initial short-circuit current in the first conduction mode without correction is measured, and the above-mentioned initial short-circuit current is corrected based on the shunt coefficient to obtain the target short-circuit current in the first conduction mode after correction. Using the shunt coefficient to correct the grounding impedance improves the accuracy of the grounding impedance, simplifies the test process, and is applicable to various short-circuit types, providing reliable data support for the design and optimization of the grounding grid.

[0068] Through the above step S102, the surface potential distribution is determined, where the surface potential distribution represents the potential change generated on the surface in the case of a short circuit in the underground cable tunnel; in step S104, according to the surface potential distribution, the first position of the current electrode for impedance measurement of the cable tunnel and the second position of the voltage electrode are determined. There is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel; in step S106, a predetermined short-circuit fault simulation method is adopted to perform current injection processing on a predetermined current injection point on the cable tunnel, obtaining a measured current at the current electrode and a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground; in step S108, based on the measured current and the measured voltage, the grounding impedance of the cable tunnel is determined. It is possible to achieve the purpose of determining the positions of the current electrode and the voltage electrode based on the surface potential change and obtaining the grounding impedance of the cable tunnel, achieving the technical effect of improving the accuracy of the measured value of the grounding impedance of the cable tunnel, and further solving the technical problem of too large electrode wiring distance in the measurement of the grounding impedance of the cable tunnel in the related art.

[0069] Based on the above embodiments and optional embodiments, the present application proposes an optional implementation manner for processing a shield-type cable tunnel in terms of its structure and measuring the grounding impedance of the shield-type cable tunnel. In the embodiments of the present application, first, two grounding grid structures of the shield-type cable tunnel are established, and the ground impedance and the surface potential distribution of these two grounding grids of the shield-type cable tunnel are calculated in detail. Secondly, aiming at the problems of large size of the cable tunnel grounding grid, long wiring length for grounding impedance test using the traditional three-pole method, and great test difficulty, starting from the layout principle of the voltage electrode and the current electrode for grounding impedance test, based on the surface potential distribution characteristics of the grounding grid of the shield-structured cable tunnel, a grounding impedance electrode layout and test method are proposed. Finally, an example verification is given for the proposed grounding impedance test method for the shield-type cable tunnel.

[0070] Figure 2 is a schematic diagram of a first shield-type cable tunnel of an optional grounding impedance determination method provided according to an embodiment of the present application, as Figure 2 shown, the shielded cable tunnel usually has the characteristics of being ultra-long and slender. The upper and lower two straight lines represent the tunnel body of the cable tunnel, and the middle annular structure is formed by splicing shield segments to form a continuous cable tunnel structure. Due to the usually ultra-long and slender characteristics of the shielded cable tunnel, its grounding grid must be able to effectively conduct the fault current into the ground while meeting the environmental requirements of the cable tunnel. Common grounding grids for shielded cable tunnels include natural grounding grids, etc. Figure 3 is a schematic diagram of a first grounding grid of a cable tunnel of an optional grounding impedance determination method provided according to an embodiment of the present application, which is a natural grounding grid model. Figure 4It is a schematic diagram of the soil stratification structure near a cable tunnel for an optional grounding impedance determination method provided by an embodiment of the present application. Figure 4 It is for Figure 3 the soil stratification structure diagram near the natural grounding grid shown in Figure 5 It is a schematic diagram of the second grounding grid of a cable tunnel for an optional grounding impedance determination method provided by an embodiment of the present application, and it is a multi-level grounding grid model.

[0071] In Figure 3 it mainly includes three parts: a cable tunnel, a grounding lead-up wire, and a substation grounding grid. The internal steel bars of the tunnel are naturally spliced into a loop to form a grounding grid, which is led into the tunnel and well-connected to the steel frame. This tunnel grounding grid model includes a long flat iron inside the tunnel and a circular grounding steel bar on the tunnel wall, and the material is steel. Both ends of the tunnel grounding grid are connected to the substation grounding grid through grounding lead-up wires. The horizontal grounding flat iron of the substation grounding grid is made of copper, with a cross-sectional size of 50 (millimeters); the vertical grounding electrode is made of steel, with a cross-sectional diameter of 25 mm. If the relative resistivity and relative permeability of copper are both set to 1, then the relative resistivity of steel is set to 10 and the relative permeability is set to 636. Figure 4 It is the soil stratification structure of this natural grounding grid. From Figure 4 it can be seen that the soil stratification structure includes a surface layer, surface soil, second-layer soil, tunnel wall concrete, and bottom soil. There is also air inside the cable tunnel. By setting the resistivity parameters of the above soil stratification structure, a semi-dry tunnel wall concrete environment is simulated, and a natural grounding grid model of the cable tunnel is constructed.

[0072] Figure 5 It is a multi-level grounding grid model of a shield-type cable tunnel. In Figure 5 it, there are multiple grounding devices. In each grounding device, vertical grounding electrodes with a depth of 3.5 m (meters) are driven underground around the shaft. The vertical grounding electrodes are connected by copper-clad steel pipes, and the grounding electrodes are led into the shaft at the shaft cover plate. The grounding lead-down wire in the shaft is placed in the shaft cavity and led down into the shield tunnel. Both the vertical grounding electrode and the horizontal grounding electrode are made of copper-clad steel material, and the grounding lead wire is made of purple copper strip. The copper-clad steel and copper-clad steel, as well as the copper-clad steel and purple copper strip, are welded using the fire clay welding technology. Through the above structure, a multi-level grounding grid model of the shield-type cable tunnel is established.

[0073] When a short-circuit fault occurs in the cable inside the cable tunnel, a large amount of short-circuit current will flow into the ground through the cable metal sheath and the grounding grid connected to it. Due to the current flowing in the ground, the surface potential will change accordingly. The surface potential distribution can be obtained through simulation.

[0074] For the above two types of shielded cable tunnel grounding grids, by selecting current injection points in the tunnel and setting current source excitation, the current dissipation scenario when a short-circuit fault occurs in the cable line in the tunnel and the current flows into the cable tunnel grounding grid is simulated. By setting a large-scale observation surface near the tunnel, the change in the surface potential near the current injection point is measured. Figure 6 It is a schematic diagram of the surface potential observation surface of an optional grounding impedance determination method provided according to an embodiment of the present application. In Figure 6 it, the thick black solid line in the middle represents the cable tunnel, and the black dots on the thick solid line represent the starting shaft, inspection shaft, and receiving shaft on the cable tunnel, which are used to place the shield machine, inspect the cable tunnel, and set up the grounding grid. The surrounding mesh structure represents the surface potential observation surface near the current injection point of the cable tunnel. By measuring the potential distribution of this observation surface, the positions of the current electrode and the voltage electrode are determined.

[0075] Inject current at a suitable current injection point in the cable tunnel to simulate the short-circuit fault of the cable tunnel, and measure the surface potential distribution to obtain the first potential distribution. According to the first potential distribution, obtain the effective distance (i.e., the target distance) between the first position where the current electrode is placed and the grounding grid. Based on the above target distance, determine the first position where the current electrode is arranged. After the current electrode is arranged, the surface potential will change, and the surface potential distribution is measured again to obtain the second surface potential distribution. According to the second potential distribution, obtain the effective distance (i.e., the target distance) between the second position where the voltage electrode is placed and the grounding grid. Based on the above target distance, determine the second position where the voltage electrode is arranged. By determining the potential distribution twice, the arrangement positions of the current electrode and the voltage electrode can be selected more accurately, thereby reducing the measurement error and ensuring the accuracy and reliability of the measurement results.

[0076] For the arrangement of the current electrode, inject current at the current injection point of the shielded cable tunnel, and measure the first surface potential and the first potential distribution of the surface mapping point of the current injection point. It can be seen from the simulation that the potential on both sides of the tunnel grounding grid drops rapidly. More than 95% of the surface potential has dropped beyond 1 km (kilometer) perpendicular distance from the current injection point. According to the first surface potential and the first predetermined potential threshold, obtain the maximum allowable surface potential in the current electrode arrangement area. Based on the maximum allowable surface potential in the current electrode arrangement area, determine the first position where the current electrode is arranged according to the first potential distribution. By accurately arranging the position of the current electrode, the influence of the current electrode on the surface potential is avoided, ensuring the accuracy of the grounding impedance measurement. At the same time, it avoids the problem of excessive test difficulty caused by the arrangement distance of the current electrode being 4-5 times the diagonal length of the grounding grid in the traditional square substation grounding grid, where the surface potential can only drop close to zero after being generally far away by 4-5 times the diagonal length of the grounding grid, resulting in excessive test difficulty in the cable tunnel grounding impedance test.

[0077] For the arrangement of voltage electrodes, after inserting the current electrode at the first position, the surface potential will change. Re-measure the surface potential to obtain the second surface potential and the second potential distribution of the surface mapping point of the current injection point. The effective range of the grounding grid refers to the change in the potential of the grounding grid caused by the arrangement of the current electrode. According to the simulation, it can be seen that when injecting current in the cable tunnel, the ground potential rise at a position 1 km vertically away from the current injection point is less than 5% of the maximum potential rise. Therefore, a current electrode is introduced here to form a test loop, reducing the influence of the introduction of the current electrode on the potential distribution of the tunnel grounding grid. After introducing the current electrode at the first position, further calculate the surface potential to obtain the second potential distribution. According to the second potential distribution, if the change in the surface potential of the tunnel is extremely small after introducing the current electrode, it indicates that the position of the current electrode is reasonable.

[0078] Based on the second surface potential and the second predetermined potential threshold, obtain the maximum allowable surface potential in the voltage electrode arrangement area. Based on the maximum allowable surface potential in the voltage electrode arrangement area, determine the second position of the voltage electrode according to the second potential distribution. Determining the second position of the voltage electrode according to the second potential distribution after introducing the current electrode can ensure that the voltage electrode is in an area close to zero potential, reducing the errors caused by mutual inductance and uneven potential distribution in voltage measurement and improving the measurement accuracy.

[0079] At the same time, since the magnetic field generated by the current electrode will directly affect the voltage electrode, causing a mutual inductance effect, the smaller the angle between the first connection line and the second connection line, the greater the electromagnetic interference caused. When determining the second position of the voltage electrode, not only the second predetermined potential threshold needs to be considered, but also the angle between the first connection line and the second connection line needs to be taken into account to determine whether this angle meets the requirements of the predetermined angle threshold. If the angle is less than the predetermined angle threshold, the second position of the voltage electrode should be adjusted to ensure that the angle between the two connection lines is large enough, thereby reducing the mutual inductance effect between the current electrode and the voltage electrode. By ensuring that the connection line angle between the current electrode and the voltage electrode is greater than the predetermined angle threshold, the mutual inductance effect between the current electrode and the voltage electrode can be significantly reduced, enabling the electrode position to more truly reflect the impedance characteristics of the grounding grid, avoiding measurement result deviations caused by improper positions of the current electrode and the voltage electrode, and thus improving the reliability of the grounding impedance test.

[0080] Therefore, the arrangement of the voltage electrode not only needs to consider the surface potential distribution, arranging the voltage electrode in the area where the surface potential is close to zero, so that the potential measured between the grounding grid and the voltage electrode, that is, the potential of the grounding grid relative to the infinite far point, controls the error within a reasonable range, but also needs to consider the angle between the first connection line and the second connection line to reduce the measurement error of the grounding impedance. From the simulation, it can be seen that on the opposite side of the tunnel near the 180 - degree line of the angle with the first connection line, at a position about 1 km away from the current injection point, the surface potential has dropped below 5% and is close to zero potential. The voltage electrode can be arranged here, and the measurement error of the grounding impedance is relatively small.

[0081] From the above analysis, it can be seen that during the test of the grounding grid of a shield tunnel, since the potential drops rapidly on both sides of the potential tunnel, neither the length of the voltage line nor the length of the current line needs to meet the condition of 4-5 times the diagonal dimension of the grounding grid. Through simulation and empirical analysis, it can be known that the current electrode and the voltage electrode can be separately arranged on both sides of the current injection point of the tunnel, at positions about 1 km perpendicular to the current injection point respectively, and at the same time, the included angle between the voltage line and the current line is close to 180°, which can meet the layout requirements of the current electrode and the voltage electrode in the grounding impedance test.

[0082] According to the size of the grounding grid of the cable tunnel, determine the predetermined distance between the current electrode and the voltage electrode. Based on the surface potential distribution, according to the requirement that the effective distances (i.e., the target distances) between the first position where the current electrode is placed and the second position where the voltage electrode is placed and the grounding grid are both less than the above-mentioned predetermined distance, determine the first position where the current electrode is placed and the second position where the voltage electrode is placed, and form an electrical connection loop between the current electrode and the voltage electrode through a wire. By scientifically selecting the layout positions of the current electrode and the voltage electrode, not only the test process of the grounding impedance of the cable tunnel is simplified, but also the accuracy and reliability of the test results are ensured.

[0083] After arranging the current electrode and the voltage electrode, based on the layout of the cable tunnel, the distribution of the cables, and the structure of the grounding grid, select the current injection point and inject current at the current injection point to simulate a predetermined short-circuit fault of the cable tunnel. When the current is injected from the current injection point, it will flow through the ground to the current electrode and form a test loop together with the voltage electrode. Measure the current at the current electrode to obtain the measured current, which is used to reflect the impedance characteristics of the grounding grid; measure the voltage at the voltage electrode to obtain the measured voltage, which is used to represent the potential change caused by the current flowing through the grounding grid and dissipating current. By simulating the short-circuit fault, the current distribution and potential change of the cable tunnel under fault conditions can be more realistically simulated, making the test results closer to the actual situation and improving the accuracy and practicality of the test.

[0084] Since different frequencies will affect the measurement results of the grounding impedance, the inductance effect, capacitance effect, and soil impedance characteristics of the grounding grid will all cause different grounding impedance measurement results when injecting the same magnitude of current at different frequencies. Therefore, when determining the short-circuit fault mode of the cable tunnel, in order to prevent power frequency interference, select multiple groups of frequency values close to the predetermined power frequency as the frequencies of current injection. Determine the predetermined current at the above-mentioned multiple groups of frequencies close to the predetermined power frequency as the injected current. Inject the above-mentioned multiple groups of predetermined currents at the frequencies close to the predetermined power frequency into the current injection point respectively, and obtain the measured current and measured voltage corresponding to multiple measurement frequencies respectively. Multi-frequency testing can cover a wider range of electrical characteristics, provide more comprehensive test results, and thus formulate a more scientific and effective cable tunnel maintenance strategy to ensure the long-term stable and safe operation of the grounding grid of the cable tunnel.

[0085] After obtaining the measured current and measured voltage corresponding to a variety of measurement frequencies, Ohm's law is used to obtain the measured impedance corresponding to the various measurement frequencies. The measured impedances corresponding to the above-mentioned multiple measurement frequencies are averaged to obtain the mean impedance. When a short circuit occurs in the cable tunnel, part of the short circuit current will be derived through the grounding grid, and part of the current will be derived through the grounding grid of the substation connected to the cable tunnel. By determining the magnitude of the above two parts of the current, the shunt coefficient of the current derived through the grounding grid is determined. Based on the above shunt coefficient, the mean impedance is corrected to obtain the grounding impedance. By correcting the mean impedance through the shunt effect coefficient, the grounding impedance of the cable tunnel can be more accurately evaluated, eliminating the interference of the substation grounding grid on the measurement results, and providing more accurate data support for system design and maintenance.

[0086] The ground impedance determination method can be applied to a software application, and the software application can adopt the strategy shown in Table 1. At the same time, the results of the software application are shown in Table 2. The specific data in Tables 1 and 2 are only examples and are not specifically limited. Figure 7 is a schematic diagram of a second shield-type cable tunnel according to an optional method for determining ground impedance provided in an embodiment of the present application. The software application can be used Figure 7 The shield-type cable tunnel shown in Figure 7 As shown, the tunnel is 4.7km long and consists of four sections of 1400m (meter), 1800m, 700m, and 800m connected in a "section hyphen" shape. Both ends of the tunnel are connected to a substation with a rated voltage of 220kv (kilovolt), and the grounding grid structure is a natural grounding grid structure composed of a full-length flat iron and a ring-shaped grounding steel bar on the tunnel wall. In the cable tunnel, there are four lines at different frequencies, namely line one, line two, line three, and line four. The traditional three-pole method is used to test the cable tunnel. The laying distance is extremely long and the difficulty is extremely great. Therefore, the method in the embodiment of the present application is used for testing.

[0087] The grounding grid model of this tunnel section was established in the simulation software, and the injection point was selected in the middle of the tunnel to simulate the short circuit fault in the tunnel. Figure 8 Schematic diagram of injection points of a second shield-type cable tunnel according to an optional method for determining ground impedance provided in an embodiment of the present application. In the figure, the thick black solid line represents the cable tunnel, and the black dots on the thick solid line represent the starting well, inspection well and receiving well on the cable tunnel. Figure 8 Shown is in the middle of the tunnel.

[0088] Table 1 shows the soil environment where the grounding grid is located. The soil impedance near the tunnel was tested on site, and the soil structure was inverted and calculated. The results are shown in Table 1. In addition, since the concrete in the tunnel is not completely dry, its resistivity is set to 400Ω·m (ohm·meter).

[0089] Table 1 Soil Environment of the Grounding Grid

[0090]

[0091] Set the injection current to 5038 A (amperes) under single-phase ground short circuit. Ignoring the grounding grids of the two-terminal substations, the impedance of the grounding grid is simulated to be 71.09 mΩ (milli-ohms). The potential near the injection point is simulated, and the change trend of the potential near the injection point is that the surface potential near the injection point is the largest, and the surrounding potential decays rapidly. According to the grounding impedance determination method proposed in the embodiment of the present application, the current electrode is selected in the area outside the action range of the grounding grid where the potential drops by more than 95%. Combining the on-site situation, the position of the current electrode is determined. After introducing the current electrode, the surface potential distribution of the tunnel is measured again, and the voltage electrode is selected in the area where the surface potential is 5% lower than the highest ground potential and close to 0, and the test results are shown in Table 2.

[0092] Table 2 Test Results

[0093]

[0094] Set Line 1, Line 2, Line 3, and Line 4 to different frequencies, and re-measure after changing the lines to reduce the error of the measurement results. After obtaining the grounding impedances at four different frequencies such as Line 1, Line 2, Line 3, and Line 4, take the average value. The test result of the average grounding impedance is 57.7 mΩ. Since the grounding grids of the two-terminal substations are ignored, calculate the shunt coefficient of the in-ground current in the tunnel, and the corrected grounding impedance is 64.1 mΩ. The simulated grounding impedance is 71.09 mΩ, with a difference of less than 10% from the on-site measurement, which proves the reliability of the test method proposed in the embodiment of the present application.

[0095] The above optional implementation manners achieve at least the following effects: By measuring the surface potential distribution near the injection point multiple times and determining the positions of the current electrode and the voltage electrode respectively, the influence of the current electrode and the voltage electrode on the surface potential distribution is reduced, the accuracy of the measurement results is improved, and the test difficulty of the grounding impedance is reduced. By measuring the grounding impedance at different frequencies and taking the average value to obtain the average impedance, the influence of different frequencies on the test accuracy of the grounding impedance is reduced, and then the average impedance is corrected using the shunt coefficient to improve the accuracy of the grounding impedance measurement results.

[0096] It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0097] In this embodiment, a ground impedance determination device is further provided. This device is used to implement the above-mentioned embodiments and preferred implementation manners, and those that have been described will not be repeated here. As used hereinafter, the terms "module" and "device" may be a combination of software and / or hardware that can achieve a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, implementation in hardware, or a combination of software and hardware is also possible and contemplated.

[0098] According to an embodiment of the present application, an embodiment of a device for implementing a ground impedance determination method is further provided. Figure 9 It is a schematic diagram of a ground impedance determination device according to an embodiment of the present application. As Figure 9 shown, the above-mentioned ground impedance determination device includes a surface potential distribution determination module 902, a position determination module 904, a measurement result determination module 906, and a ground impedance determination module 908. The device will be described below.

[0099] The surface potential distribution determination module 902 is used to determine the surface potential distribution, where the surface potential distribution represents the potential change on the ground when a short circuit occurs in the underground cable tunnel.

[0100] The position determination module 904 is connected to the surface potential distribution determination module 902 and is used to determine the first position of the current electrode for impedance measurement of the cable tunnel and the second position of the voltage electrode according to the surface potential distribution. There is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel.

[0101] The measurement result determination module 906 is connected to the position determination module 904 and is used to perform current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method, obtain a measured current at the current electrode, and obtain a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground.

[0102] The ground impedance determination module 908 is connected to the measurement result determination module 906 and is used to determine the ground impedance of the cable tunnel based on the measured current and the measured voltage.

[0103] In a ground impedance determination device provided by an embodiment of the present application, a surface potential distribution determination module 902 is provided to determine the surface potential distribution, where the surface potential distribution represents the potential change generated on the surface in the case of a short circuit in an underground cable tunnel; a position determination module 904 is connected to the surface potential distribution determination module 902 to determine a first position of a current electrode for impedance measurement of the cable tunnel and a second position of a voltage electrode according to the surface potential distribution. There is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel; a measurement result determination module 906 is connected to the position determination module 904 to perform current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method, obtain a measured current at the current electrode, and obtain a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground; a ground impedance determination module 908 is connected to the measurement result determination module 906 to determine the ground impedance of the cable tunnel based on the measured current and the measured voltage. The purpose of determining the positions of the current electrode and the voltage electrode based on the surface potential change and obtaining the ground impedance of the cable tunnel is achieved, and the technical effect of improving the accuracy of the measured value of the ground impedance of an ultra-long and slender shield-type cable tunnel is realized. Furthermore, the technical problem of excessive electrode wiring distance in the measurement of the ground impedance of a cable tunnel in the related art is solved.

[0104] It should be noted that the above-mentioned various modules can be implemented by software or hardware. For example, for the latter, it can be implemented in the following manner: the above-mentioned various modules can be located in the same processor; or, the above-mentioned various modules are located in different processors in any combination.

[0105] It should be noted here that the above-mentioned surface potential distribution determination module 902, position determination module 904, measurement result determination 906, and ground impedance determination module 908 correspond to steps S102 to step S108 in the embodiment. The examples and application scenarios implemented by the above-mentioned modules and the corresponding steps are the same, but are not limited to the content disclosed in the above-mentioned embodiment. It should be noted that the above-mentioned modules can run in a computer terminal as a part of the device.

[0106] It should be noted that the optional or preferred implementation manners of this embodiment can refer to the relevant descriptions in the embodiment, and will not be repeated here.

[0107] The above-mentioned ground impedance determination device may further include a processor and a memory. The surface potential distribution determination module 902, position determination module 904, measurement result determination module 906, ground impedance determination module 908, etc. are all stored in the memory as program units, and the above-mentioned program units stored in the memory are executed by the processor to implement corresponding functions.

[0108] The processor contains a kernel, which retrieves the corresponding program unit from the memory. One or more kernels can be set. The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of, for example, read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0109] An embodiment of the present application provides a non-volatile storage medium, on which a program is stored, and when the program is executed by a processor, a ground impedance determination method is implemented.

[0110] An embodiment of the present application provides an electronic device, which includes a processor, a memory, and a program stored on the memory and executable on the processor. When the processor executes the program, the following steps are implemented: determining the surface potential distribution, where the surface potential distribution represents the potential change on the surface when a short circuit occurs in the underground cable tunnel; determining the first position of the current electrode and the second position of the voltage electrode for impedance measurement of the cable tunnel according to the surface potential distribution, where there is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel; performing current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method to obtain a measured current at the current electrode and a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground; determining the grounding impedance of the cable tunnel based on the measured current and the measured voltage. The device herein can be a server, a PC, etc.

[0111] The present application also provides a computer program product, which, when executed on a data processing device, is adapted to execute a program initialized with the following method steps: determining the surface potential distribution, where the surface potential distribution represents the potential change on the surface when a short circuit occurs in the underground cable tunnel; determining the first position of the current electrode and the second position of the voltage electrode for impedance measurement of the cable tunnel according to the surface potential distribution, where there is an electrical connection loop between the current electrode and the voltage electrode, and the target distance between the first position and the second position is less than a predetermined distance, and the predetermined distance is determined based on the size of the grounding grid of the cable tunnel; performing current injection processing on a predetermined current injection point on the cable tunnel by using a predetermined short-circuit fault simulation method to obtain a measured current at the current electrode and a measured voltage at the voltage electrode, where the current injection point forms a loop with the current electrode and the voltage electrode through the ground; determining the grounding impedance of the cable tunnel based on the measured current and the measured voltage.

[0112] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0113] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0114] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means implements the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0115] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0116] In a typical configuration, a computing device includes one or more processors (CPUs), an input / output interface, a network interface, and memory.

[0117] The memory may include non-permanent memory in a computer-readable medium, in the form of random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0118] A computer-readable medium includes both permanent and non-permanent, removable and non-removable media and can implement information storage by any method or technology. The information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory, or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD), or other optical storage, magnetic cassette tapes, magnetic tape disk storage, or other magnetic storage devices, or any other non-transitory medium that can be used to store information that can be accessed by a computing device. As defined herein, a computer-readable medium does not include transitory computer-readable media, such as modulated data signals and carrier waves.

[0119] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0120] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, system, or computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0121] The above are only embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A method for determining ground impedance, characterized in that: include: Determining a surface potential distribution, wherein the surface potential distribution represents a potential change on the surface of the earth when a short circuit occurs in an underground cable tunnel; Determine, according to the surface potential distribution, a first position of a current electrode for performing impedance measurement on a cable tunnel, and a second position of a voltage electrode, wherein an electrical connection loop exists between the current electrode and the voltage electrode, and a target distance between the first position and the second position is less than a predetermined distance, wherein the predetermined distance is determined based on a grounding grid size of the cable tunnel; Using a predetermined short-circuit fault simulation method, current injection processing is performed on a predetermined flow injection point on the cable tunnel, a measured current is obtained at the current electrode, and a measured voltage is obtained at the voltage electrode, wherein the flow injection point forms a loop with the current electrode and the voltage electrode through the earth; Based on the measured current and the measured voltage, a ground impedance of the cable tunnel is determined.

2. The method according to claim 1, characterized in that The surface potential distribution includes a first potential distribution and a second potential distribution, and determining a first position of a current electrode for performing impedance measurement on a cable tunnel and a second position of a voltage electrode according to the surface potential distribution includes: Performing current injection processing on the injection point to determine the first potential distribution; determining the first position of the current electrode according to the first potential distribution; determining the second potential distribution when the current electrode is inserted into the first position; The second position of the voltage pole is determined according to the second potential distribution.

3. The method according to claim 2, characterized in that Determining the first position of the current electrode according to the first potential distribution includes: Determine a first surface potential corresponding to a surface mapping point of the injection point; Based on the first potential distribution, the first position at which the first surface potential is reduced to a first predetermined potential threshold is determined.

4. The method according to claim 2, characterized in that: Determining the second position of the voltage electrode according to the second potential distribution includes: Determine a second surface potential corresponding to the surface mapping point of the injection point, wherein the second surface potential is determined when the current electrode is inserted into the first position; Based on the second potential distribution, the second position at which the second surface potential is reduced to a second predetermined potential threshold is determined.

5. The method according to claim 1, characterized in that An angle between a first line connecting the first position and the surface mapping point of the injection point and a second line connecting the second position and the surface mapping point is greater than a predetermined angle threshold.

6. The method according to any one of claims 1 to 5, characterized in that The method of adopting a predetermined short-circuit fault simulation mode to perform current injection processing on a predetermined current injection point on the cable tunnel, obtaining a measured current at the current pole, and obtaining a measured voltage at the voltage pole, comprises: According to the short-circuit fault simulation method, determining predetermined currents at multiple measurement frequencies, wherein the multiple measurement frequencies are determined to avoid power frequency interference; The predetermined currents at the multiple measurement frequencies are used to perform current injection processing on the injection point to obtain measurement currents and measurement voltages corresponding to the multiple measurement frequencies respectively.

7. The method according to claim 6, characterized in that The determining the ground impedance of the cable tunnel based on the measured current and the measured voltage comprises: Determining the measurement impedances corresponding to the multiple measurement frequencies respectively according to the measurement currents and measurement voltages corresponding to the multiple measurement frequencies respectively; Performing average processing on the measured impedances corresponding to the multiple measurement frequencies to obtain average impedance; Based on the mean impedance, the ground impedance is determined.

8. The method according to claim 7, characterized in that The short-circuit current in the cable tunnel is also derived through a grounding grid of a substation connected to the cable tunnel. The determining of the grounding impedance based on the mean impedance includes: Determining a current splitting coefficient based on the short-circuit current derived from the grounding grid of the cable tunnel and the short-circuit current derived from the grounding grid of the substation; The mean impedance is corrected according to the shunt coefficient to determine the ground impedance.

9. A device for determining ground impedance, characterized in that: include: A surface potential distribution determination module, used to determine the surface potential distribution, wherein the surface potential distribution represents the potential change generated on the surface when a short circuit occurs in an underground cable tunnel; a position determination module, configured to determine, according to the surface potential distribution, a first position of a current electrode for performing impedance measurement on a cable tunnel, and a second position of a voltage electrode, wherein an electrical connection loop exists between the current electrode and the voltage electrode, and a target distance between the first position and the second position is less than a predetermined distance, wherein the predetermined distance is determined based on a grounding grid size of the cable tunnel; a measurement result determination module, configured to use a predetermined short-circuit fault simulation method to perform current injection processing on a predetermined flow injection point on the cable tunnel, obtain a measured current at the current electrode, and obtain a measured voltage at the voltage electrode, wherein the flow injection point forms a loop with the current electrode and the voltage electrode through the earth; The ground impedance determination module is used to determine the ground impedance of the cable tunnel based on the measured current and the measured voltage.

10. An electronic device, characterized in that: include: One or more processors and a memory, wherein the memory is used to store one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the ground impedance determination method described in any one of claims 1 to 8.

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